Reinforced flexible films have been utilized for the fabrication of tension structures as used in buildings, sails for sailing vessels, parachutes, balloons, inflatable structures and other structures for many years. These structures have traditionally been fabricated by joining together flat pieces of fabric or film or reinforced film where the joining seam has a curvature that imparts a complex curvature onto the finished assembly. More recently, methods have been developed to fabricate these types of products where a three dimensional mold is used to laminate a reinforced film in its final three dimensional curvature.
Large flexible membranes with spherical or smoothly varying complex curvature are generally comprised of long slender membrane pieces joined along their edges where each piece is referred to as a gore. In the cases of balloons and yacht sails as used in off-wind applications, the membrane must also support a pressure differential normal to its surface. To support this pressure differential, these membranes are designed with complex three dimensional curvature and sufficient structural integrity. In the case of large research balloons, the gores run from pole to pole (bottom to top), are fabricated from a thin film and may include fiber or other reinforcement to enhance structural and barrier properties while containing low weight.
The prior art includes a product and a method to manufacture a three dimensional flexible laminated composite that requires a mold that is at least the size of the largest laminate piece to be fabricated, upon which each layer of the laminate is laid down in sequence and then subject to lamination forces to produce a three dimensional flexible laminate. An overhead gantry is utilized to lay down reinforcing fibers along arbitrary trajectories upon the mold surface. If very large pieces of laminate are to made, the machine and the mold have to be of an equally large size.
The prior art also discloses a method to fabricate laminated flexible composites that utilizes a rotating cylindrical mold upon which the laminate is synthesized from film and fiber. The mold is comprised of a rigid cylindrical structure that can rotate under programmed control upon which are located a large number of independent radially adjustable actuators. The actuators support a flexible outer surface that is generally cylindrical, but can be deformed by the actuators to define a surface with complex curvature upon which film and fiber can be laminated to produce reinforced flexible films on a continuous basis.
The above examples have been utilized extensively for yacht sail manufacture and prototype work has been performed on tension structures and high altitude balloon pieces. Both processes contemplate the demands of shaping complex structures with significant Gaussian curvature. As a result each process requires a mold with fully independent actuators and further requires a large number of actuators. In one example, an adjustable cylindrical mold has adjustable actuators which are activated one axial row at a time as the mold turns. Each row is set to its position and stays in that position until the fabricated web is released at a later point around the arc of the mold. Along each row are disposed a number of radial actuators so that each row can have a complex and unique profile. These profiles when taken together form a complex three dimensional surface where each row is normally different from all of the other rows around the drum.